Structures for deploying electrode elements

ABSTRACT

An electrode support structure comprises a guide body having at its distal end a flexible spline leg. The spline leg is flexed to define an arcuate shape to facilitate intimate contact against tissue. An electrode element is carried by the spline leg for movement along its axis. The structure includes a control element coupled to the electrode element. The control element remotely imparts force to move the electrode element along the axis of the spline leg. Therefore, in use, the physician can cause the electrode element to travel along a path that the spline leg defines, without otherwise changing the location of the guide body.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 08/321,424,filed Oct. 11, 1994, now U.S. Pat. No. 5,885,278, which is acontinuation-in-part of application Ser. No. 08/320,198, filed Oct. 7,1994, now abandoned.

FIELD OF THE INVENTION

The invention relates to systems and methods for ablating myocardialtissue for the treatment of cardiac conditions.

BACKGROUND OF THE INVENTION

Normal sinus rhythm of the heart begins with the sinoatrial node (or "SAnode") generating an electrical impulse. The impulse usually propagatesuniformly across the right and left atria and the atrial septum to theatrioventricular node (or "AV node"). This propagation causes the atriato contract.

The AV node regulates the propagation delay to the atrioventricularbundle (or "HIS" bundle). This coordination of the electrical activityof the heart causes atrial systole during ventricular diastole. This, inturn, improves the mechanical function of the heart.

Today, as many as 3 million Americans experience atrial fibrillation andatrial flutter. These people experience an unpleasant, irregular heartbeat, called arrhythmia. Because of a loss of atrioventricularsynchrony, these people also suffer the consequences of impairedhemodynamics and loss of cardiac efficiency. They are more at risk ofstroke and other thromboembolic complications because of loss ofeffective contraction and atrial stasis.

Treatment is available for atrial fibrillation and atrial flutter.Still, the treatment is far from perfect.

For example, certain antiarrhythmic drugs, like quinidine andprocainamide, can reduce both the incidence and the duration of atrialfibrillation episodes. Yet, these drugs often fail to maintain sinusrhythm in the patient.

Cardioactive drugs, like digitalis, Beta blockers, and calcium channelblockers, can also be given to control the ventricular response.However, many people are intolerant to such drugs.

Anticoagulant therapy also combats thromboembolic complications.

Still, these pharmacologic remedies often do not remedy the subjectivesymptoms associated with an irregular heartbeat. They also do notrestore cardiac hemodynamics to normal and remove the risk ofthromboembolism.

Many believe that the only way to really treat all three detrimentalresults of atrial fibrillation and flutter is to actively interrupt allthe potential pathways for atrial reentry circuits.

James L. Cox, M.D. and his colleagues at Washington University (St.Louis, Mo.) have pioneered an open heart surgical procedure for treatingatrial fibrillation, called the "maze procedure." The procedure makes aprescribed pattern of incisions to anatomically create a convolutedpath, or maze, for electrical propagation within the left and rightatria, therefore its name. The incisions direct the electrical impulsefrom the SA node along a specified route through all regions of bothatria, causing uniform contraction required for normal atrial transportfunction. The incisions finally direct the impulse to the AV node toactivate the ventricles, restoring normal atrioventricular synchrony.The incisions are also carefully placed to interrupt the conductionroutes of the most common reentry circuits.

The maze procedure has been found very effective in curing atrialfibrillation. Yet, despite its considerable clinical success, the mazeprocedure is technically difficult to do. It requires open heart surgeryand is very expensive. Because of these factors, only a few mazeprocedures are done each year.

It is believed the treatment of atrial fibrillation and flutter requiresthe formation of long, thin lesions of different lengths and curvilinearshapes in heart tissue. Such long, thin lesion patterns require thedeployment within the heart of flexible ablating elements havingmultiple ablating regions. The formation of these lesions by ablationcan provide the same therapeutic benefits that the complex incisionpatterns that the surgical maze procedure presently provides, butwithout invasive, open heart surgery.

With larger and/or longer multiple electrode elements comes the demandfor more precise control of the ablating process. The delivery ofablating energy must be governed to avoid incidences of tissue damageand coagulum formation. The delivery of ablating energy must also becarefully controlled to assure the formation of uniform and continuouslesions, without hot spots and gaps forming in the ablated tissue.

The task is made more difficult because heart chambers vary in size fromindividual to individual. They also vary according to the condition ofthe patient. One common effect of heart disease is the enlargement ofthe heart chambers. For example, in a heart experiencing atrialfibrillation, the size of the atrium can be up to three times that of anormal atrium.

One objective of the invention is to provide tissue ablation systems andmethods providing beneficial therapeutic results without requiringinvasive surgical procedures.

Another objective of the invention is to provide systems and methodsthat simplify the creation of complex lesions patterns in body tissue,such as in the heart.

SUMMARY OF THE INVENTION

A principal objective of the invention is to provide improved structuresand methodologies for deploying electrode elements in contact withtissue. In a preferred implementation, the structures and methodologiesthat embody features of the invention make possible the creation oflong, thin lesion patterns in tissue for the treatment of, for example,heart conditions like atrial fibrillation or atrial flutter.

In achieving these objectives, the invention provides an electrodesupport structure comprising a guide body having at its distal end aflexible spline leg. The spline leg is flexed to define an arcuate shapeto facilitate intimate contact against tissue. An electrode element iscarried by the spline leg for movement along its axis. The structureincludes a control element coupled to the electrode element. The controlelement remotely imparts force to move the electrode element along theaxis of the spline leg. Therefore, in use, the physician can cause theelectrode element to travel along a path that the spline leg defines,without otherwise changing the location of the guide body.

The invention also provides a method for ablating tissue in a heart. Themethod introduces a probe into the heart. The probe carries at least oneelongated spline leg flexed outward of the probe to define an arcuateshape. The probe also includes at least one ablation electrode that ismovable along the at least one spline leg spline in response to theapplication of force. The method established contact between theablation electrode and a region of heart tissue, along which the splineleg defines an elongated path. The method transmits ablation energy tothe ablation electrode while in contact with the tissue region. Themethod also applies force to move the ablation electrode along the atleast one spline leg, while maintaining contact with the tissue, toablate tissue along the elongated path.

Other features and advantages of the inventions are set forth in thefollowing Description and Drawings, as well as in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of an ablation probe having a full-loop structurefor supporting multiple ablation elements;

FIG. 2 is an elevation view of a spline used to form the loop structureshown in FIG. 1;

FIG. 3 is an elevation view of the distal hub used to form the loopstructure shown in FIG. 1;

FIG. 4 is a side section view of the hub shown in FIG. 3;

FIG. 5 is a perspective, partially exploded view of the spline, distalhub, and base assembly used to form the loop structure shown in FIG. 1;

FIG. 6A is an enlarged perspective view of the base assembly shown inFIG. 5;

FIG. 6B is a side section view of an alternative base assembly for theloop structure shown in FIG. 1;

FIG. 7 is an elevation view of a half-loop structure for supportingmultiple electrodes;

FIG. 8 is an elevation view of a composite loop structure for supportingmultiple electrodes comprising two circumferentially spaced half-loopstructures;

FIG. 9 is an elevation view of a composite loop structure comprising twofull-loop structures;

FIG. 10 is an elevation view, with parts broken away, of multipleelectrode elements comprising segmented rings carried by a loop supportstructure;

FIG. 11A is an enlarged view, with parts broken away, of multipleelectrode elements comprising wrapped coils carried by a loop supportstructure;

FIG. 11B is an elevation view, with parts broken away, of multipleelectrode elements comprising wrapped coils carried by a loop supportstructure;

FIG. 12 is a top view of a steering mechanism used to deflect the distalend of the probe shown in FIG. 1;

FIG. 13 is a plan view of a full-loop structure for supporting multipleelectrode elements having an associated center stylet attached to aremote control knob for movement to extend and distend the full-loopstructure;

FIG. 14 is a side section view of the remote control knob for the centerstylet shown in FIG. 13;

FIG. 15 is a plan view of the full-loop structure shown in FIG. 13, withthe control knob moved to extend the full-loop structure;

FIG. 16 is a plan view of a full-loop structure shown in FIG. 13, withthe control handle moves to distend the full-loop structure;

FIG. 17 is a plan view of a half-loop structure for supporting multipleelectrode elements having an associated center stylet attached to aremote control knob for movement to extend and distend the half-loopstructure;

FIG. 18 is a plan view of the half-loop structure shown in FIG. 17, withthe control knob moved to extend the half-loop structure;

FIG. 19 is a plan view of a half-loop structure shown in FIG. 17, withthe control handle moves to distend the half-loop structure;

FIG. 20 is a plan view of a full-loop structure for supporting multipleelectrode elements having an associated center stylet attached to aremote control knob for movement to extend and distend the full-loopstructure, and also having a remotely controlled steering mechanism toflex the center stylet to bend the full-loop structure into acurvilinear shape;

FIG. 21 is a side elevation view of the full-loop structure shown inFIG. 20;

FIG. 22 is an enlarged sectional view, generally taken along line 22--22in FIG. 20, showing the steering wires attached to the center stylet toflex it;

FIGS. 23A and 23B are side elevation views showing the operation of thesteering mechanism in bending the full-loop structure, respectively, tothe left and to the right;

FIG. 24 is a largely diagrammatic, perspective view of the full-loopstructure bent to the right, as also shown in side elevation in FIG.23B;

FIG. 25 is a plan view of the full-loop structure shown in FIG. 20 andthe associated remote control knob for extending and distending as wellas bending the full-loop structure;

FIG. 26 is a side section view, taken generally along lines 26--26 inFIG. 25, of the control knob for extending and distending as well asbending the full-loop structure;

FIG. 27 is a largely diagrammatic, perspective view of the full-loopstructure when distended and bent to the right;

FIG. 28 is a largely diagrammatic, perspective view of a half-loopstructure with steerable center stylet bent to the right;

FIG. 29 is a plan, partially diagrammatic, view of a full-loop structurefor supporting multiple electrode elements having a movable spline legattached to a remote control knob for movement to extend and distend thefull-loop structure;

FIG. 30A is a section view, taken generally along line 30A--30A in FIG.29, of the interior of the catheter body lumen, through which themovable spline leg passes;

FIG. 30B is a side section view of an alternative way of securing thefull-loop structure shown in FIG. 29 to the distal end of the cathetertube;

FIG. 31 is a plan, partially diagrammatic view of the full-loopstructure shown in FIG. 29 being extended by pulling the movable splineleg inward;

FIGS. 32 and 33 are plan, partially diagrammatic views of the full-loopstructure shown in FIG. 29 being distended by pushing the movable splineleg outward;

FIGS. 34 and 35 are largely diagrammatic views of the full-loopstructure shown in FIG. 29 being distended by pushing the movable splineleg outward while deployed in the atrium of a heart;

FIGS. 36, 37, and 38 are plan, partially diagrammatic views of afull-loop structure for supporting multiple electrode elements havingtwo movable spline legs attached to remote control knobs for coordinatedmovement to extend and distend the full-loop structure;

FIG. 39A is a plan view of a full-loop structure for support multipleelectrode elements having a smaller, secondary loop structure formed inone spline leg;

FIG. 39B is a side view of the full-loop structure shown in FIG. 39A,showing the smaller, secondary loop structure;

FIG. 40A is a perspective view of a modified full-loop structure forsupporting multiple electrode elements having an odd number of three ormore spline legs;

FIG. 40B is a top section view of the base of the full-loop structureshown in FIG. 40A;

FIGS. 41, 42, and 43 are plan, partially diagrammatic, views of abifurcated full-loop structure for supporting multiple electrodeelements having movable half-loop structures to extend and distend thebifurcated full-loop structure;

FIGS. 44 and 45 are plan, partially diagrammatic, views of analternative form of a bifurcated full-loop structure for supportingmultiple electrode elements having movable center ring to extend anddistend the bifurcated full-loop structure;

FIG. 46 is a plan, partially diagrammatic, views of an alternative formof a bifurcated full-loop structure for supporting multiple electrodeelements having both a movable center ring and movable spline legs toextend and distend the bifurcated full-loop structure;

FIGS. 47, 48, and 49 are plan, partially diagrammatic, views of anotheralternative form of a bifurcated full-loop structure for supportingmultiple electrode elements having movable half-loop structures toextend and distend the bifurcated full-loop structure;

FIG. 50 is a plan view of a full-loop structure for supporting andguiding a movable electrode element;

FIG. 51 is a side elevation view of the full-loop structure and movableelectrode element shown in FIG. 50;

FIG. 52 is an enlarged view of the movable electrode supported andguided by the structure shown in FIG. 50, comprising wound coils wrappedabout a core body;

FIG. 53 is an enlarged view of another movable electrode that can besupported and guided by the structure shown in FIG. 50, comprisingbipolar pairs of electrodes;

FIG. 54 is a largely diagrammatic view of the full-loop structure andmovable electrode element shown in FIG. 50 in use within the atrium of aheart;

FIG. 55 is a perspective, elevation view of a bundled loop structure forsupporting multiple electrode elements, comprising an array ofindividual spline legs structures, each having a movable portion thatindependently extends and distends the individual structures to shapeand flex the overall bundled loop structure;

FIG. 56 is a top view of the bundled loop structure shown in FIG. 55;

FIG. 57 is a perspective elevation view of the bundled loop structureshown in FIG. 55 with some of the independently movable spline legsextended and distended to change the flexure of the bundled loopstructure;

FIG. 58 is a top view of the bundled loop structure shown in FIG. 57;

FIGS. 59A and 59B are, respectively, top and side views of a bundledloop structure like that shown in FIG. 55 in position within an atrium,out of contact with the surrounding atrial wall;

FIGS. 60A and 60B are, respectively, top and side views of a bundledloop structure like that shown in FIG. 57, with some of theindependently movable spline legs extended and distended to change theflexure of the bundled loop structure, to bring it into contact with thesurrounding atrial wall; and

FIG. 61 is a top section view of the base of the bundled loop structureshown in FIG. 55.

The invention may be embodied in several forms without departing fromits spirit or essential characteristics. The scope of the invention isdefined in the appended claims, rather than in the specific descriptionpreceding them. All embodiments that fall within the meaning and rangeof equivalency of the claims are therefore intended to be embraced bythe claims.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

This Specification discloses multiple electrode structures that embodyaspects the invention. This Specification also discloses tissue ablationsystems and techniques using multiple temperature sensing elements thatembody other aspects of the invention. The illustrated and preferredembodiments discuss these structures, systems, and techniques in thecontext of catheter-based cardiac ablation. That is because thesestructures, systems, and techniques are well suited for use in the fieldof cardiac ablation.

Still, it should be appreciated that the invention is applicable for usein other tissue ablation applications. For example, the various aspectsof the invention have application in procedures for ablating tissue inthe prostrate, brain, gall bladder, uterus, and other regions of thebody, using systems that are not necessarily catheter-based.

I. Loop support structures for Multiple Electrodes

FIG. 1 shows a multiple electrode probe 10 that includes a loopstructure 20 carrying multiple electrode elements 28.

The probe 10 includes a flexible catheter tube 12 with a proximal end 14and a distal end 16. The proximal end 14 carries an attached handle 18.The distal end 16 carries a loop structure 20 that supports multipleelectrodes.

In FIG. 1, the loop support structure 20 comprises two flexible splinelegs 22 spaced. diametrically opposite each other. The dual leg loopstructure 20 shown in FIG. 1 will be called a "full-loop" structure.

The far ends of the spline legs 22 radiates from a distal hub 24. Thenear ends of the spline legs 22 radiate from a base 26 attached to thedistal end 16 of the catheter tube 12. The multiple electrode elements28 are arranged along each spline leg 22.

In one implementation, the two spline legs 22 of the structure 20 arepaired together in an integral loop body 42 (see FIG. 2). Each body 42includes a mid-section 44 from which the spline elements 22 extend as anopposed pair of legs. As FIG. 2 shows, the mid-section 44 includes apreformed notch or detent 46, whose function will be described later.

The loop body 42 is preferably made from resilient, inert wire, likeNickel Titanium (commercially available as Nitinol material). However,resilient injection molded inert plastic or stainless steel can also beused. Preferably, the spline legs 22 comprise thin, rectilinear stripsof resilient metal or plastic material. Still, other cross sectionalconfigurations can be used.

In this implementation (see FIGS. 3 and 4), the distal hub 24 has agenerally cylindrical side wall 50 and a rounded end wall 52. Alongitudinal slot 56 extends through the hub 24, diametrically acrossthe center bore 54.

In the illustrated embodiment, the hub 24 is made of an inert, machinedmetal, like stainless steel. The bore 54 and slot 56 can be formed byconventional EDM techniques. Still, inert molded plastic materials canbe used to form the hub 24 and associated openings.

In this implementation, to assemble the structure 20 (see FIGS. 4 and5), a spline leg 22 of the hoop-like body 42 is inserted through theslot 56 until the mid-body section 44 enters the bore 54. The detent 46snaps into the bore 54 (see FIG. 4) to lock the body 42 to the hub 24,with the opposed pair of spline legs 22 on the body 42 radiating free ofthe slot 56 (see FIG. 5).

In the illustrated embodiment (see FIGS. 5 and 6A), the base 26 includesan anchor member 62 and a mating lock ring 64. The anchor member 62 fitswith an interference friction fit into the distal end 16 of the cathetertube 12. The lock ring 64 includes a series of circumferentially spacedgrooves 66 into which the free ends of the spline legs 22 fit. The lockring 64 fits about the anchor member 62 to capture with an interferencefit the free ends of the spline legs 22 between the interior surface ofthe grooves 66 and the outer surface of the anchor member 62 (see FIG.6). The anchor member 62/lock ring 64 assembly holds the spline elements22 in a desired flexed condition.

In an alternative construction (see FIG. 6B), the base 26 can comprise aslotted anchor 63 carried by the distal end 16 of the catheter tube 12.The slotted anchor 63 is made of an inert machined metal or moldedplastic material. The slotted anchor 63 includes an outer ring 65 and aconcentric slotted inner wall 67. The interior of the anchor 63 definesan open lumen 226 to accommodate passage of wires and the like betweenthe catheter tube bore 36 and the support structure 20 (as will bedescribed in greater detail later).

The inner wall 67 includes horizontal and vertical slots 69 and 71 forreceiving the free ends of the spline legs 22. The free ends passthrough the horizontal slots 69 and are doubled back upon themselves andwedged within the vertical slots 71 between the outer ring 65 and theinner wall 67, thereby securing the spline legs 22 to the anchor 63.

There are other alternative ways of securing the spline legs 22 to thedistal end 16 of the catheter tube 12, which will be described later.

Preferably, the full-loop structure 20 shown in FIG. 1 does not includea hub 24 like that shown in FIGS. 1 and 3, and, in addition, does notincorporate a detented integral loop body 42 like that shown in FIG. 2.Any single full-loop structure without a center stiffener or stylet (aswill be described later) preferably comprises a single length ofresilient inert wire (like Nickel Titanium) bent back upon itself andpreformed with resilient memory to form the desired full loop shape.Structure 112 in FIG. 29 (which will be described in greater detaillater) exemplifies the use of a preshaped doubled-back wire to form aloop, without the use of a hub 24 or detented loop body 42. FIGS. 10 and11B also show a portion of the doubled-back wire embodiment, free of thehub 24.

FIG. 7 shows an alternative loop structure 20(1) that includes a singlespline leg 22(1) carrying multiple electrode elements 28. This singleleg loop structure will be called a "half-loop" structure, in contrastto the dual leg loop structure 20 (i.e., the "full-loop" structure)shown in FIG. 1.

In assembling the half-loop structure 20(1) shown in FIG. 7, thehoop-like body 42 shown in FIG. 2 is cut on one side of the detent 46 tofore the single spline leg 22(1). The single spline leg 22(1) issnap-fitted into the hub 24 and captured with an interference fit by theanchor member 62/lock ring 64 assembly of the base 26 in the manner justdescribed (shown in FIGS. 5 and 6A). Alternatively, the single splineleg 22(1) can be wedged within the base anchor ring 63 shown in FIG. 6B.In FIG. 7, the half-loop structure 20(1) also includes a centerstiffener 40 secured to the base 26 and to the bore 54 of the hub 24.The stiffener 40 can be made of a flexible plastic like Fortron, or froma hollow tube like hypo-tubing or braid plastic tubing.

It should be appreciated that other loop-type configurations besides thefull-loop structure 20 and half-loop structure 20(1) are possible. Forexample, two half-loop structures 20(1), one or both carrying electrodeelements 28, can be situated in circumferentially spaced apart positionswith a center stiffener 40, as FIG. 8 shows. As another example, fourhalf-loop structures, or two full-loop structures can be assembled toform a three-dimensional, basket-like structure 60 (without using acenter stiffener 40), like that shown in FIG. 9.

Regardless of the configuration, the loop structure provides theresilient support necessary to establish and maintain contact betweenthe electrode elements 28 and tissue within the body.

The electrode elements 28 can serve different purposes. For example, theelectrode elements 28 can be used to sense electrical events in hearttissue. In the illustrated and preferred embodiments, the principal useof the electrode elements 28 is to emit electrical energy to ablatetissue. In the preferred embodiments, the electrode elements 28 areconditioned to emit electromagnetic radio frequency energy.

The electrode elements 28 can be assembled in various ways.

In one preferred embodiment (see FIG. 10), the elements comprisemultiple, generally rigid electrode elements 30 arranged in a spacedapart, segmented relationship upon a flexible, electricallynonconductive sleeve 32 which surrounds the underlying spline leg 22.The sleeve 32 is made a polymeric, electrically nonconductive material,like polyethylene or polyurethane.

The segmented electrodes 30 comprise solid rings of conductive material,like platinum. The electrode rings 30 are pressure fitted about thesleeve 32. The flexible portions of the sleeve 32 between the rings 30comprise electrically nonconductive regions. Alternatively, theelectrode segments 30 can comprise a conductive material, likeplatinum-iridium or gold, coated upon the sleeve 32 using conventionalcoating techniques or an ion beam assisted deposition (IBAD) process.For better adherence, an undercoating of nickel or titanium can beapplied. The electrode coating can be applied either as discrete,closely spaced segments or in a single elongated section.

In a more preferred embodiment (see FIGS. 11A and 11B), spaced apartlengths of closely wound, spiral coils are wrapped about the sleeve 32to form an array of segmented, generally flexible electrodes 34. Thecoil electrodes 34 are made of electrically conducting material, likecopper alloy, platinum, or stainless steel. The electrically conductingmaterial of the coil electrode 34 can be further coated withplatinum-iridium or gold to improve its conduction properties andbiocompatibility.

The inherent flexible nature of a coiled electrode structures 34 alsomakes possible the construction of a continuous flexible ablatingelement comprising an elongated, closely wound, spiral coil ofelectrically conducting material, like copper alloy, platinum, orstainless steel, wrapped about all or a substantial length of theflexible sleeve 32.

The electrode elements 28 can be present on all spline legs 22, as FIG.1 shows, or merely on a selected number of the spline legs 22, with thisremaining spline legs serving to add structural strength and integrityto the structure.

The electrode elements 28 are electrically coupled to individual wires58 (see FIG. 11A) to conduct ablating energy to them. The wires 58extend along the associated spline leg 22 (as FIG. 11A shows), through asuitable access opening provided in the base 24 (for example, the anchorlumen 226 shown in FIG. 6B) into and through the catheter body lumen 36(as generally shown in FIG. 1 and FIGS. 30A/B), and into the handle 18,where they are electrically coupled to external connectors 38 (see FIG.1). The connectors 38 plug into a source of RF ablation energy (notshown).

Various access techniques can be used to introduce the probe 10 and itsloop support structure 20 into the desired region of the heart. Forexample, to enter the right atrium, the physician can direct the probe10 through a conventional vascular introducer through the femoral vein.For entry into the left atrium, the physician can direct the probe 10through a conventional vascular introducer retrograde through the aorticand mitral valves.

Alternatively, the physician can use the delivery system shown inpending U.S. application Ser. No. 08/033,641, filed Mar. 16, 1993, andentitled "Systems and Methods Using Guide Sheaths for Introducing,Deploying, and Stabilizing Cardiac Mapping and Ablation Probes."

In use, the physician verifies contact between the electrode elements 28and heart tissue using conventional pacing and sensing techniques. Oncethe physician establishes contact with tissue in the desired heartregion, the physician applies ablating energy to the electrode elements28.

The electrode elements 28 can be operated in a uni-polar mode, in whichthe ablation energy emitted by the electrode elements 28 is returnedthrough an indifferent patch electrode attached to the skin of thepatient (not shown). Alternatively, the elements 28 can be operated in abi-polar mode, in which ablation energy emitted by one element 28 isreturned through another element 28 on the spline leg 22.

The size and spacing of the electrode elements 28 shown in FIGS. 10 and11A/B are well suited for creating continuous, long and thin lesionpatterns in tissue when ablation energy is applied simultaneously toadjacent emitting electrode elements 28. Continuous lesion patternsuniformly result when adjacent electrode elements 28 (i.e., the segments30 or coils 34) are spaced no farther than about 2.5 times the electrodesegment diameter apart. Further details of the formation of continuous,long and thin lesion patterns are found in copending U.S. patentapplication Ser. No. 08/287,192, filed Aug. 8, 1994, entitled "Systemsand Methods for Forming Elongated Lesion Patterns in Body Tissue UsingStraight or Curvilinear Electrode Elements," which is incorporatedherein by reference.

Using rigid electrode segments 30, the length of the each electrodesegment can vary from about 2 mm to about 10 mm. Using multiple rigidelectrode segments longer than about 10 mm each adversely effects theoverall flexibility of the element. Generally speaking, adjacentelectrode segments 30 having lengths of less than about 2 mm do notconsistently form the desired continuous lesion patterns.

When flexible electrode segments 34 are used, electrode segments longerthat about 10 mm in length can be used. Flexible electrode segments 34can be as long as 50 mm. If desired, the flexible electrode structure 34can extend uninterrupted along the entire length of the support spline22.

The diameter of the electrode segments 30 or 34 and underlying splineleg 22 (including the flexible sleeve 32) can vary from about 2 Frenchto about 10 French.

Preferably (as FIGS. 10 and 11B show), the side of the ablation elements28 that, in use, is exposed to the blood pool is preferably covered witha coating 48 of an electrically and thermally insulating material. Thiscoating 48 can be applied, for example, by brushing on a UV-typeadhesive or by dipping in polytetrafluoroethylene (PTFE) material.

The coating 48 prevents the transmission of ablating energy directlyinto the blood pool. Instead, the coating 48 directs the appliedablating energy directly toward and into the tissue.

The focused application of ablating energy that the coating 48 provideshelps to control the characteristics of the lesion. The coating 48 alsominimizes the convective cooling effects of the blood pool upon theablation element while ablating energy is being applied, thereby furtherenhancing the efficiency of the lesion formation process.

In the illustrated and preferred embodiments (see FIGS. 10 and 11A/B),each flexible ablation element carries at least one and, preferably, atleast two, temperature sensing elements 68. The multiple temperaturesensing elements 68 measure temperatures along the length of theelectrode element 28. The temperature sensing elements 68 ca comprisethermistors or thermocouples.

An external temperature processing element (not shown) receives andanalyses the signals from the multiple temperature sensing elements 68in prescribed ways to govern the application of ablating energy to theflexible ablation element. The ablating energy is applied to maintaingenerally uniform temperature conditions along the length of theelement.

Further details of the use of multiple temperature sensing elements intissue ablation can be found in copending U.S. patent application Ser.No. 08/286,930, filed Aug. 8, 1994, entitled "Systems and Methods forControlling Tissue Ablation Using Multiple Temperature SensingElements."

To aid in locating the structure 20 within the body, the handle 16 andcatheter body 12 preferably carry a steering mechanism 70 (see FIGS. 1and 12) for selectively bending or flexing the distal end 16 of thecatheter body 12.

The steering mechanism 18 can vary. In the illustrated embodiment (seeFIG. 12), the steering mechanism 70 includes a rotating cam wheel 72with an external steering lever 74 (see FIG. 1). As FIG. 12 shows, thecam wheel 72 holds the proximal ends of right and left steering wires76. The steering wires 76, like the signal wires 58, pass through thecatheter body lumen 36. The steering wires 76 connect to the left andright sides of a resilient bendable wire or spring (not shown) enclosedwithin the distal end 16 of the catheter body 12. Forward movement ofthe steering lever 74 flexes or curves the distal end 16 down. Rearwardmovement of the steering lever 74 flexes or curves the distal end 16 up.

Further details of this and other types of steering mechanisms are shownin Lundquist and Thompson U.S. Pat. No. 5,254,088, which is incorporatedinto this Specification by reference.

II. Variable Shape Loop Support Structures

To uniformly create long, thin lesions having the desired therapeuticeffect, the loop support structure 20 or 20(1) must make and maintainintimate contact between the electrode elements 28 and the endocardium.

The invention provides loop support structures that the physician canadjust to adapt to differing physiologic environments.

A. Distended Loop Structures

The adjustable loop structure 78 shown in FIG. 13 is in many respectssimilar to the full-loop structure 20 shown in FIG. 1. The adjustablefull-loop structure 78 includes the pair of diametrically oppositespline legs 22 that radiate from the base 26 and hub 24.

In addition, the adjustable full-loop structure 78 includes a flexiblestylet 80 attached at its distal end to the hub bore 54. The stylet 80can be made from a flexible plastic material, like Fortron, or from ahollow tube, like hypo-tubing or braid plastic tubing.

The stylet 80 extends along the axis of the structure 78, through thebase 26 and catheter body lumen 36, and into the handle 18. In thisarrangement, the stylet 80 is free to slide fore and aft along the axisof the catheter body 12.

The proximal end of the stylet 80 attaches to a control knob 82 in thehandle 18 (as FIG. 13 shows). The control knob 82 moves within a grooves84 (see FIGS. 13 and 14) in the handle 18 to impart fore and aftmovement to the stylet 80. Stylet movement changes the flexure of thestructure 78.

Forward movement of the stylet 80 (i.e., toward the distal end 16)pushes the hub 24 away from the base 26 (see FIG. 15). The loopstructure 78 elongates as the spline legs 22 straighten and moveradially inward, to the extent permitted by the resilience of the splinelegs 22. With the spline legs 22 straightened, the loop structure 78presents a relatively compact profile to facilitate vascularintroduction.

Rearward movement of the stylet 80 (i.e., toward the distal end 16)pulls the hub 24 toward the base 26 (see FIG. 16). The spline legs 22bend inward in the vicinity of the hub 24, while the remainder of thesplines, constrained by the base, distend. The loop structure 78 bowsradially out to assume what can be called a "heart" shape.

When the structure 78 is positioned within the atrium 88 of a heart inthe condition shown in FIG. 16, the stylet 80 compresses the spline legs22, making them expand or bow radially. The expansion presses thedistended midportion of the spline legs 22 (and the electrode elements28 they carry) symmetrically against opposite walls 86 of the atrium 88.The symmetric expansion of the outwardly bowed spline legs 22 pressesthe opposite atrial walls 86 apart (as FIG. 16 shows), as the radialdimension of the loop structure 78 expands to span the atrium 88.

The symmetric expansion presses the electrode elements 28 into intimatesurface contact against the endocardium. The symmetric expansionstabilizes the position of the loop structure 78 within the atrium 88.The resilience of the spline legs 22, further compressed by thepulled-back stylet 80, maintains intimate contact between the electrodeelements 28 and atrial tissue, without trauma, as the heart expands andcontracts.

As FIGS. 17 to 19 show, the push-pull stylet 80 can also be used inassociation with a half-loop structure 90, like that previously shownand discussed in FIG. 7. In this arrangement, the movable stylet 80substitutes for the flexible, but otherwise fixed stiffener 40.

In this arrangement, pushing the stylet 80 forward (as FIG. 18 shows)elongates the half-loop structure 90 for vascular introduction. Pullingthe stylet 80 rearward (as FIG. 19 shows) bows the single, spline leg 22of the structure outward, expanding it so that more secure contact canbe achieved against the atrial wall 86, or wherever tissue contact isdesired.

B. Curvilinear Loop structures

FIGS. 20 and 21 show a full-loop structure 92 that includes a centerstylet 94, which can be flexed. The flexing of the center stylet 94bends the spline legs 22 in a second direction different than the radialdirection in which they are normally flexed. In the illustratedembodiment, this second direction is generally perpendicular to the axesof the spline legs 22, as FIGS. 23A/B and 24 show, although acute bendsthat are not generally perpendicular can also be made. The bending ofthe spline legs 22 in this fashion makes possible the formation of long,thin curvilinear lesions using a full-loop structure 92, or (as will bedescribed later) in a half-loop structure 110, as well.

The stylet 94 itself can be either fixed in position between the hub 24and the base 26, or movable along the axis of the loop structure 92 toextend and distend the radial dimensions of the spline legs 22 in themanner already described (see FIGS. 15 and 16). In the illustrated andpreferred embodiment, the stylet 94 slides to alter the radialdimensions of the structure.

In one implementation, as FIG. 22 best shows, the stylet 94 is made froma metal material, for example stainless steel 17-7, Elgiloy™ material,or Nickel Titanium material. A pair of left and right steering wires,respectively 96(R) and 96(L) is attached to opposite side surfaces ofthe stylet 94 near the hub 24, by adhesive, soldering, or by suitablemechanical means. The steering wires 96(R) and 96(L) are attached to thestylet side surfaces in a diametric opposite orientation that is atright angles to the radial orientation of the spline legs 22 relative tothe stylet 94.

The steering wires 96(R) and 96(L) extend along the stylet 94, throughthe base 26 and catheter body lumen 36, and into the handle 18 (see FIG.25). Preferable, as FIG. 22 best shows, a tube 98 surrounds the stylet94 and steering wires 96(R) and 96(L), at least along the distal,exposed part of the stylet 94 within the structure 92, keeping them in aclose relationship. The tube 98 can be heat shrunk to fit closely aboutthe stylet 94 and steering wires 96(R) and 96(L).

As FIGS. 25 and 26 show, a groove 100 in the handle carries a controlassembly 102. The stylet 94 is attached to the control assembly 102, inthe manner already described with respect to the control knob 82 inFIGS. 13 and 14. Sliding movement of the control assembly 102 within thegroove 100 imparts fore and aft movement to the stylet 94, therebydistending or extending the loop structure 92.

The control assembly 102 further includes a cam wheel 104 (see FIG. 26)rotatable about an axle on the control assembly 102 in response to forceapplied to an external steering lever 108. The cam wheel 104 holds theproximal ends of the steering wires 96(R) and 96(L), in the mannerdisclosed in Lundquist and Thompson U.S. Pat. No. 5,254,088, alreadydiscussed, which is incorporated herein by reference.

Twisting the steering lever 108 counterclockwise applies tension to theleft steering wire 96(L), bending the loop structure 92 to the left (asFIG. 23A shows). The electrode elements 28 (which in FIGS. 20 to 27comprises a continuous coil electrode 34, described earlier) likewisebend to the left.

Similarly, twisting the steering lever 108 clockwise applies tension tothe right steering wire 96(R), bending the loop structure 92 to theright (as FIGS. 23B and 24 show). The electrode elements 28 likewisebend to the right.

The bent electrode elements 28, conforming to the bent spline legs 22,assume different curvilinear shapes, depending upon amount of tensionapplied by the steering wires 96(R) and 96(L). When contacting tissue,the bent electrode elements 28 form long, thin lesions in curvilinearpatterns.

In an alternative implementation, the stylet 94 is not flexible andremotely steerable, but is instead made of a malleable metal material,like annealed stainless steel. In this arrangement, before deployment inthe body, the physician applies external pressure to manually bend thestylet 94 into a desired shape, thereby imparting a desired curvilinearshape to the electrode elements of the associated loop structure. Themalleable material of the stylet 94 retains the preformed shape, untilthe associated loop structure is withdrawn from the body and sufficientexternal pressure is again applied by the physician to alter the styletshape.

In addition to having a malleable stylet 94, the splines 22 themselvescan also be made of a malleable material, like annealed stainless steel,or untreated stainless steel 17-7, or untreated Nickel Titanium. In oneimplementation, the most distal parts of the malleable splines 22 areheat treated to maintain their shape and not collapse duringintroduction and deployment in the vascular system. This will also givethe overall structure greater stiffness for better contact with thetissue. It also gives the physician the opportunity to bend thestructure to form long, thin, lesions in prescribed curvilinear patternsset by the malleable splines.

Whether flexible and remotely flexed during deployment, or malleable andmanually flexed before deployment, by further adjusting the fore-and-aftposition of the stylet 94, the physician can also control the radialdimensions of the loop structure 94 in concert with controlling thecurvilinear shape of the loop structure 92, as FIG. 27 shows. A diversearray of radial sizes and curvilinear shapes is thereby available.

As FIG. 28 shows, a half-loop structure 110 can also include a fixed ormovable stylet 94 with steering wires 96(R) and 96(L). The use of thesame handle-mounted control assembly 102/rotatable can 104 assemblyshown in FIGS. 25 and 26 in association with the half-loop structure 110makes possible the creation of diverse curvilinear shapes of variableradii. Alternatively, a malleable stylet 94 and malleable splines can beused.

C. Loop Structures with Movable Spline Legs

FIGS. 29 to 35 show a full-loop structure 112 in which only one splineleg 114 is attached to the base 26. The fixed spline leg 114 ispreformed with resilient memory to assume a curve of a selected maximumradius (shown in FIG. 33). The other spline leg 116, locateddiametrically opposed to the fixed spline leg 114, extends through thebase 26 and catheter body lumen 36 (see FIGS. 30A and 30B) into thehandle 18. The spline leg 116 slides fore and aft with respect to thebase 26. Movement of the spline leg 116 changes the flexure of thestructure 112.

The full-loop structure 112 shown in FIGS. 29 to 35 need not include ahub 24 like that shown in FIGS. 1 and 3, and, in addition, need notincorporate a detented integral loop body 42 like that shown in FIG. 2.Any single full-loop structure without a center stiffener or stylet,like the structure 112 in FIG. 29, can comprise a single length of wirebent back upon itself and preformed with resilient memory to form thedesired full loop shape. For the same reason, the single full-loopstructure 20 shown in FIG. 1 can, in an alternative construction, bemade without a hub 24 and a detented loop body 42, and instead employ apreshaped doubled-back wire to form a loop, like the structure 20.

FIG. 30B shows an alternative way of securing the fixed spline leg 114to the distal end 16 of the catheter tube 12, without using a base 26.In this embodiment, the free end of the fixed spline leg 114 liesagainst the interior of the tube 12. The leg 114 passes through a slit115 formed in the catheter tube 12. The leg 114 is bent back upon itselfin a u-shape to lie against the exterior of the tube 12, wedging thetube 12 within the u-shape bend 117. A sleeve 119 is heat shrunk aboutthe exterior of the tube 12 over the region where the u-shape bend 117of the spline leg 114 lies, securing it to the tube 12. Alternatively, ametallic ring (not shown) can be used to secure the spline leg 114 tothe tube 12. The movable spline leg 116 and wires 58 pass through theinterior bore 36 of the catheter tube 12, as before described.

The proximal end of the spline leg 116 (see FIG. 29) is attached to amovable control knob 82 carried in a groove 84 on the handle 18, likethat shown in FIG. 13. Movement of the control knob 82 within the groove84 thereby imparts fore-and-aft movement to the spline leg 116.

In the illustrated embodiment, the fixed spline leg 114 carrieselectrode elements 28 in the manner already described. The movablespline leg 116 is free of electrode elements 28. Still, it should beappreciated that the movable spline leg 116 could carry one or moreelectrode elements 28, too.

As FIGS. 31 to 33 show, moving the control knob 82 forward slides themovable spline leg 116 outward, and vice versa. The movable spline leg116 applies a counter force against the resilient memory of the fixedspline leg 114, changing the flexure and shape of the loop structure 112for vascular introduction and deployment in contact with tissue. Bypulling the movable spline leg 116 inward (as FIG. 31 shows), thecounter force contracts the radius of curvature of the fixed spline leg114 against its resilient memory. Pushing the movable spline leg 116outward (as FIGS. 32 and 33 show) allows the resilient memory of thefixed spline leg 114 to expand the radius of curvature until theselected maximum radius is achieved. The counter force applied changesthe flexure and shapes the fixed spline leg 114 and the electrodeelements 28 it carries to establish and maintain more secure, intimatecontact against atrial tissue.

The magnitude (designated V in FIGS. 31 to 33) of the counter force, andthe resulting flexure and shape of the loop structure 112, variesaccording to extent of outward extension of the movable spline leg 116.Pulling the movable spline leg 116 progressively inward (therebyshortening its exposed length) (as FIG. 31 shows) contracts the loopstructure 112, lessening its diameter and directing the counter forceprogressively toward the distal end of the structure. Pushing themovable spline leg 116 progressively outward (thereby lengthening itsexposed length) (as FIGS. 32 and 33 show) progressively expands the loopstructure 112 in response to the resilient memory of the fixed splineleg 114, increasing its diameter and directing the counter forceprogressively away from the distal end of the structure.

As FIGS. 34 and 35 show, by manipulating the movable spline leg 116, thephysician can adjust the flexure and shape of the loop structure 112within the atrium 88 from one that fails to make sufficient surfacecontact between the electrode element 28 and the atrial wall 86 (as FIG.34 shows) to one that creates an extended region of surface contact withthe atrial wall 86 (as FIG. 35 shows).

FIGS. 36 to 38 show a full-loop structure 1113 in which each spline leg120 and 122 is independently movable fore and aft with respect to thebase 26. In the illustrated embodiment, both spline legs 120 and 122carry electrode elements 28 in the manner already described.

In this arrangement, the handle 18 includes two independently operable,sliding control knobs 124 and 126 (shown diagrammatically in FIGS. 36 to38), each one attached to a movable spline leg 120/122, to impartindependent movement to the spline legs 120/122 (as shown by arrows inFIGS. 36 to 38). Each spline leg 120/122 is preformed with resilientmemory to achieve a desired radius of curvature, thereby imparting aresilient curvature or shape to the full-loop structure 118 itself.Coordinated opposed movement of both spline legs 120/122 (as FIGS. 37and 38 show) using the control knobs 124/126 allows the physician toelongate the curvature of the loop structure 118 into more of an ovalshape, compared to more circular loop structures 112 formed using asingle movable leg 116, as FIGS. 31 to 33 show.

FIGS. 39A and 39B show an alternative full-loop structure 128 having onespline leg 130 that is fixed to the base 26 and another spline leg 132,located diametrically opposed to the fixed spline 130, that is movablefore and aft with respect to the base 26 in the manner alreadydescribed. The movable spline leg 132 can carry electrode elements 28(as FIG. 39A shows), or be free of electrode elements, depending uponthe preference of the physician.

In the structure shown in FIGS. 39A and 39B, the fixed spline leg 130branches in its midportion to form a smaller, secondary full-loopstructure 134 that carries electrode elements 28. In the embodimentshown in FIGS. 39A and 39B, the secondary loop structure 134 lies in aplane that is generally perpendicular to the plane of the main full-loopstructure 128.

The smaller, secondary full-loop structure 134 makes possible theformation of annular or circumferential lesion patterns encircling, forexample, accessory pathways, atrial appendages, and the pulmonary veinwithin the heart. In the illustrated embodiment, the movable spline leg132 compresses the secondary full-loop structure 134, urging andmaintaining it in intimate contact with the targeted tissue area.

FIGS. 39A and 39B therefore show a compound flexible support forelectrode elements. While the primary support structure 128 and thesecondary support structure 134 are shown as full loops, it should beappreciated that other arcuate or non-arcuate shapes can be incorporatedinto a compound structure. The compound primary structure 128 integratedwith a secondary structure 134 need not include a movable spline leg,or, if desired, both spline legs can be movable. Furthermore, a centerstylet to contract and distend the main structure 128 can also beincorporated, with or without a stylet steering mechanism.

FIGS. 40A and B show a modified full-loop structure 216 having an oddnumber of spline legs 218, 220, and 222. The structure 216 includes twospline legs 218 and 220 that, in the illustrated embodiment, are fixedto the base 26 about 120° apart from each other. As FIG. 40B shows, thebase 26 is generally like that shown in FIG. 6B, with the slotted anchor63 in which the near ends of the legs 218 and 220 are doubled back andwedged. The structure 216 also includes a third spline leg 222 that, inthe illustrated embodiment, is spaced about 120° from the fixed splinelegs 218/220. As FIG. 40B shows, the near end of the third spline leg222 is not attached to the base 26, but passes through the inner lumen226 into the lumen 36 of the catheter tube 12. The third spline leg 222is thereby movable fore and aft with respect to the base 26 in themanner already described. Alternatively, all spline legs 218, 220, and222 can be fixed to the base 26, or more than one spline leg can be mademoveable.

A hub 24 like that shown in FIGS. 3 and 4 includes circumferentiallyspaced slots 56 to accommodate the attachment of the three splines 218,220, and 222.

The fixed splines 218 and 220 carry electrode elements 28 (as FIG. 40Ashows), while the movable spline 22 is free of electrode elements. AsFIG. 40B show, the wires 58 coupled to the electrode elements 28 passthrough the anchor lumen 226 for transit through the catheter tube bore36. The orientation of the fixed splines 218 and 220 relative to themovable spline 222 thereby presents an ablation loop 224, like thesecondary loop structure 134 shown in FIGS. 39A/B, that lies in a planethat is generally transverse of the plane of the movable spline 222. Ofcourse, other orientations of an odd number of three or more spline legscan be used.

The movable spline leg 222 extends and compresses the secondarystructure 134 to urge and maintain it in intimate contact with thetargeted tissue area. Of course, a center stylet to further contract anddistend the ablation loop 224 can also be incorporated, with or withouta stylet steering mechanism.

D. Bifurcated Loop Structures

FIGS. 41, 42, and 43 show a variation of a loop structure, which will becalled a bifurcated full-loop structure 136. The structure 136 (see FIG.41) includes two oppositely spaced splines legs 138 and 140, eachcarrying one or more electrode elements 28. The near end of each splineleg 138/140 is attached to the base 26. The far end of each spline leg138/140 is attached a stylet 142 and 144. Each spline leg 138/140 ispreformed with resilient memory to achieve a desired maximum radius ofcurvature (which FIG. 41 shows).

The spline leg stylets 142/144 are joined through a junction 146 to acommon control stylet 148. The common control stylet 148 passes throughthe catheter body lumen 36 to a suitable slidable control knob 150 inthe handle 18, as already described. By sliding, the control knob 150moves the control stylet 148 to change the flexure of the spline legs138/140.

When the control stylet 148 is fully withdrawn, as FIG. 41 shows, thejunction 146 is located near the base 26 of the structure 136, and thespline legs 138/140 assume their preformed maximum radii of curvatures.The spline legs 138/140 form individual half-loop structures (like shownin FIG. 7) that together emulate a full-loop structure (like that shownin FIG. 1), except for the presence of a connecting, distal hub 24.

Forward movement of the control stylet 148 first moves the junction 146within the confines of the structure 136, as FIG. 42 shows. The forwardmovement of the control stylet 148 is translated by the spline legstylets 142/144 to urge the spline legs 138/140 apart. The distal end ofthe bifurcated structure 136 opens like a clam shell.

As the spline legs 138/140 separate, they distend. The control stylet150 thus compresses the splines legs 138/140 to press them into contactwith the tissue area along opposite sides of the structure 136. In thisway, the bifurcated structure 136 emulates the full-loop structure 78,when distended (as FIG. 16 shows).

Continued forward movement of the control stylet 150 (as FIG. 43 shows)moves the junction 146 and attached spline leg stylets 142/146 outbeyond the confines of the structure 136. This continued forwardmovement extends the spline legs 136/140, while moving them radiallyinward. This, in effect, collapses the bifurcated structure 136 into arelatively low profile configuration for vascular introduction. In thisway, the bifurcated structure 136 emulates the full-loop structure 78,when elongated (as FIG. 15 shows).

FIGS. 44 and 45 show an alternative embodiment of a bifurcated full-loopstructure 152. The structure 152 includes two oppositely spaced splinelegs 154/156, each carrying one or more electrode elements 28, like thestructure 136 shown in FIGS. 41 to 43. Each spline leg 154/156 ispreformed with a resilient memory to assume a desired maximum radius ofcurvature (which FIG. 44 shows).

Unlike the structure 136 shown in FIGS. 41 to 43, the structure 152shown in FIGS. 44 and 45 fixes both ends of the spline legs 154/156 tothe base 26. The spline legs 154/156 thereby form stationary,side-by-side half-loop structures, each with an inner portion 158 and anouter portion 160. Together, the stationary half-loop structures createthe bifurcated full-loop structure 152.

In this arrangement, a center stylet 162 is attached to a ring 164 thatcommonly encircles the inner portions 158 of the spline legs 154/156along the center of the structure 152. Movement of the stylet 162 slidesthe ring 164 along the inner leg portions 158. The stylet 162 passesthrough the catheter body lumen 36 to a suitable control in the handle(not shown), as already described.

Forward movement of the ring 164 (as FIG. 45 shows) jointly extends thespline legs 154/156, creating a low profile for vascular introduction.Rearward movement of the ring 164 (as FIG. 44 shows) allows theresilient memory of the preformed spline legs 154/156 to bow the legs154/156 outward into the desired loop shape.

FIG. 46 shows another alternative embodiment of a bifurcated full-loopstructure 166. This structure 166 has two oppositely spaced spline legs168 and 170, each carrying one or more electrode elements 28. Eachspline leg 168/170 is preformed with a resilient memory to assume amaximum radius of curvature (which FIG. 46 shows).

The near end of each spline leg 168/170 is attached to the base 26. Thefar end of each spline leg 168/170 is individually attached to its ownstylet 172/174. Instead of joining a common junction (as in thestructure 136 shown in FIGS. 41 to 43), the spline stylets 172/174 ofthe structure 166 individually pass through the catheter body lumen 36to suitable control knobs (not shown) in the handle 18. Like theembodiment shown in FIGS. 44 and 45, a third stylet 176 is attached to aring 178 that encircles the spline stylets 172 and 174. The third stylet176 passes through the guide tube lumen 36 to its own suitable controlknob (not shown) in the handle 18.

The embodiment shown in FIG. 46 allows the physician to move the ring178 up and down along the spline stylets 172 and 174 to shape and changethe flexure of the structure 166 in the manner shown in FIGS. 44 and 45.Independent of this, the physician can also individually move the splinestylets 172 and 174 to further shape and change the flexure of eachspline leg 168 and 170, as in the case of the movable spline legs120/122 shown in FIGS. 36 to 38. This structure 166 thus gives thephysician latitude in shaping the loop structure to achieve the desiredcontact with the atrial wall.

Another alternative embodiment of a bifurcated full-loop structure 180is shown in FIGS. 47 to 49. In this embodiment, the structure 180includes two oppositely spaced spline legs 182 and 184, each carryingone or more electrode elements 28. Each spline leg 182/184 is preformedwith a resilient memory to assume a desired maximum radius of curvature(which FIG. 49 shows).

The inner portion 186 of each spline leg 182/184 is attached to the base26. A stationary ring 190 encircles the inner portions 186 near thedistal end of the structure 180, holding them together.

The outer portion 188 of each spline leg 182/184 is free of attachmentto the base 26 and is resiliently biased away from the base 26. Eachouter portion 188 is individually attached to its own stylet 192 and194. The spline stylets 192 and 194 individually pass through thecatheter body lumen 36 to suitable control knobs (not shown) in thehandle 18.

Pulling the spline legs stylets 192/194 rearward pulls the outer portion188 of the attached spline leg 182/184 radially toward the base 26,against their resilient memories, creating a low profile suitable forvascular access (as FIG. 47 shows). Pushing the spline stylets 192/194forward pushes the outer portion 188 of the attached spline leg 182/184,aided by the resilient memory of the spline leg 182/184, outward (asFIGS. 48 and 49 show). The spline stylets 192/194 can be manipulatedtogether or individually to achieve the shape and flexure desired.

E. Loop support Structures for Movable Electrodes

FIGS. 50 and 51 show a full-loop structure 196 which supports a movableablation element 198. The structure 196 includes a pair of spline legs200 secured at their distal ends to the hub 24 and at their proximalends to the base 26, in the manner described in association with thestructure shown in FIG. 1. A center stiffener 202 extends between thebase 26 and the hub 24 to lend further strength.

The ablation element 198 (see FIG. 52) comprises a core body 204 made ofan electrically insulating material. The body 204 includes a centrallumen 26, through which one of the spline legs 200 passes. The core body204 slides along the spline leg 200 (as shown by arrows in FIGS. 50 to52).

In the illustrated and preferred embodiment (see FIG. 52), a coilelectrode element 34 (as already described) is wound about the core body204. Alternatively, the core body 204 can be coated with an electricallyconducting material or have an electrically conducting metal bandfastened to it. As shown in FIG. 53, the ablation element can alsocomprise a composite structure 198(1) (see FIG. 53) of two bi-polarelectrodes 208 separated by an electrically insulating material 210. Thecore body 204 of the electrode can range in diameter from 3 Fr to 8 Frand in length from 3 mm to 10 mm.

A guide wire 212 is attached to at least one end of the ablationelectrode 198 (see FIGS. 50 and 52). The guide wire 212 extends from thehandle 18 through the catheter body lumen 36, along the center stiffener202 and through the hub 24 for attachment to the ablation element 198. Asignal wire 214 also extends in common along the guide wire 212 (seeFIG. 52) to supply ablation energy to the electrode 198. The proximalend of the guide wire 212 is attached to a suitable control knob (notshown) in the handle 18. Movement of the guide wire 212 forward pushesthe ablation element 198 along the spline leg 200 from the distal end ofthe structure 196 to the proximal end.

Two guide wires (212 and 213) may be used (as FIG. 52 shows), which areattached to opposite ends of the ablation element 198. Pulling on oneguide wire 212 advances the electrode 198 toward the distal end of thestructure 196, while pulling on the other guide wire 213 advances theelectrode 198 in the opposite direction toward the proximal end of thestructure 196. In an alternative implementation (not shown), the distaltip of a second catheter body can be detachably coupled eithermagnetically or mechanically to the movable electrode 198. In thisimplementation, the physician manipulates the distal end of the secondcatheter body into attachment with the electrode 198, and then uses thesecond catheter body to drag the electrode 198 along the structure 196.

In use (as FIG. 54 shows), once satisfactory contact has beenestablished with the atrial wall 86, sliding the ablation electrode 198along the spline leg 200 while applying ablation energy creates a longand thin lesion pattern. The ablation can be accomplished by eithermoving the electrode 198 sequentially to closely spaced locations andmaking a single lesion at each location, or by making one continuouslesion by dragging the electrode 198 along the tissue while ablating.

One or both spline legs 200 can also be movable with respect to thebase, as before described, to assure intimate contact between theablation element 198 and the endocardium.

F. Bundled Loop Structures

The invention makes possible the assembly of bundled, independentlyadjustable loop structures to form a dynamic three dimensional electrodesupport structure 228, like that shown in FIGS. 55 to 58.

The structure 228 shown in FIGS. 55 to 58 comprises four spline legs(designated L1, L2, L3, and L4) circumferentially spaced ninety degreesapart. Each spline leg L1, L2, L3, and L4 is generally like that shownin FIG. 29. Each leg L1, L2, L3, and L4 is preformed with resilientmemory to assume a curve of selected maximum radius. In the illustratedembodiment, each leg L1 to L4 carries at least one electrode element 28,although one or more of the legs L1 to L4 could be free of electrodeelements 28.

The outer portions 230 of each spline leg L1 to L4 are attached to thestructure base 26. As FIG. 61 shows, the base 26 is similar to thatshown in FIG. 26, having an outer ring 236 and a concentric slottedinner element 238, through which the near ends of the outer spline legportions 230 extend. The near ends are doubled back upon themselves andwedged in the space 240 between the outer ring 236 and inner element238, as earlier shown in FIG. 6B.

The inner portions 232 of each spline leg L1, L2, L3, and L4 are notattached to the base 26. They pass through lumens 242 in the innerelement 238 of the base 26 (see FIG. 61) and into catheter body lumen 36for individual attachment to control knobs 234 on the handle 18 (seeFIG. 55). Wires 58 associated with the electrode elements 28 carried byeach leg L1 to L4 pass through other lumens 244 in the inner element 238(see FIG. 61).

The inner portion 232 of each spline leg L1 to L4 is independentlymovable, in the same way as the spline leg shown in FIGS. 31 to 35. Bymanipulating the control knobs 234, the physician can change this normalflexure of the structure 228 (which FIGS. 55 and 56 show) to a newflexure (which FIGS. 57 and 58 show), by altering the shape each splineleg L1 to L4 independent of each other. As FIGS. 57 and 5B show, theinner portion 232 of leg L4 has been pulled aft, compressing theassociated loop. The inner portion 232 of leg L2 has been pushedforward, expanding the associated loop.

As FIGS. 59A/B and 60A/B show, by selective manipulation of the movableinner portions 232 of the spline legs L1 to L4, the physician can adjustthe shape of the three dimensional loop structure 228 within the atrium88 from one that fails to make sufficient surface contact between theelectrode element 28 and the atrial wall 86 (as FIGS. 59A/B show) to onethat expands the atrium 88 and creates an extended region of surfacecontact with the atrial wall 86 (as FIGS. 60A/60B show). The physiciancan thereby tailor the shape of the three dimensional structure 228 tothe particular physiology of the patient.

In an alternative arrangement, the inner portions 232 of the spline legsL1 to L4 can be fixed to the base 26 and the outer portions 230 madefree to move in the manner shown in FIGS. 47 to 49.

III. Conclusion

It should be now be apparent that one or more movable spline legs can beused in association with a movable center stylet to provide control ofthe shape and flexure of the ablation element. The further inclusion ofsteering wires on the movable stylet, or the use of a malleable styletand/or malleable spline legs adds the ability to form curvilinear lesionpatterns.

It is thereby possible to combine in a single loop support structure oneor more movable spline legs (as FIGS. 31 to 38 show), a movable centerstylet (as FIGS. 13 to 19 show), and a stylet steering assembly ormalleable stylet/splines (as FIGS. 20 to 28 show). Such a structure iscapable of creating a diverse number of shapes and contact forces toreliably achieve the type and degree of contact desired between theablation elements and the targeted tissue area, despite physiologicdifferences among patients.

It should also be appreciated that the invention is applicable for usein tissue ablation applications that are not catheter-based. Forexample, any of the loop structures like those described in thisapplication can be mounted at the end of hand-held probe for directplacement by the physician in contact with a targeted tissue area. Forexample, a hand held loop structure carrying multiple electrodes can bemanipulated by a physician to ablate tissue during open heart surgeryfor mitral valve replacement.

Various features of the invention are set forth in the following claims.

What is claimed is:
 1. An apparatus, comprising:a carrier defining alongitudinal axis; a basket structure including a plurality of resilientshape memory splines having a normally curved configuration carried bythe carrier, the resilient shape memory splines being arranged relativeto one another such that the basket is asymmetric about the longitudinalaxis defined by the carrier; and at least one electrode on at least oneof the resilient shape memory splines.
 2. An apparatus as claimed inclaim 1, wherein the carrier comprises a catheter.
 3. An apparatus asclaimed in claim 1, wherein the plurality of resilient shape memorysplines comprises two shape memory splines.
 4. An apparatus as claimedin claim 1, wherein the resilient shape memory splines define distalportions, the apparatus further comprising:a center stiffener associatedwith the distal portions of the plurality of resilient shape memorysplines.
 5. An apparatus as claimed in claim 1, wherein the at least oneelectrode comprises a plurality of electrodes on each resilient shapememory spline.
 6. An apparatus as claimed in claim 1, wherein theplurality of resilient shape memory splines comprises at least threeresilient shape memory splines, the at least one electrode comprises aplurality of electrodes on at least two of the resilient shape memorysplines, and there are no electrodes on at least one resilient shapememory spline.
 7. An apparatus as claimed in claim 1, wherein theplurality of resilient shape memory splines comprises at least fourresilient shape memory splines.
 8. An apparatus, comprising:a carrierdefining a longitudinal axis; a basket structure including a pluralityof resilient shape memory splines having a normally curved configurationcarried by the carrier, each spline in the basket structure passingthrough a common plane oriented perpendicular to the longitudinal axisdefined by the carrier, the resilient shape memory splines beingarranged relative to one another such that when the common plane isdivided into a number of equal sectors equal to the number of splines,each sector having a corner that intersects the longitudinal axisdefined by the carrier, the basket structure can be oriented such thatat least one of the sectors will have more resilient shape memorysplines passing therethrough than at least one of the other sectors; andat least one electrode on at least one of the resilient shape memorysplines.
 9. An apparatus as claimed in claim 8, wherein the carriercomprises a catheter.
 10. An apparatus as claimed in claim 8, whereinthe plurality of resilient shape memory splines comprises two shapememory splines.
 11. An apparatus as claimed in claim 8, wherein theresilient shape memory splines define distal portions, the apparatusfurther comprising:a center stiffener associated with the distalportions of the plurality of resilient shape memory splines.
 12. Anapparatus as claimed in claim 8, wherein the at least one electrodecomprises a plurality of electrodes on each resilient shape memoryspline.
 13. An apparatus as claimed in claim 8, wherein the plurality ofresilient shape memory splines comprises at least four resilient shapememory splines.
 14. An apparatus, comprising:a carrier defining alongitudinal axis; a basket structure including a plurality of resilientshape memory splines having a normally curved configuration carried bythe carrier, each spline in the basket structure passing through acommon plane oriented perpendicular to the longitudinal axis defined bythe carrier, the resilient shape memory splines being arranged relativeto one another such that when the common plane is divided into fourequal quadrants, each quadrant having a corner that intersects thelongitudinal axis defined by the carrier, at least one of the quadrantswill have more resilient shape memory splines passing therethrough thanat least one of the other quadrants and there will be no resilient shapememory splines located in at least two of the quadrants; and at leastone electrode on at least one of the resilient shape memory splines. 15.An apparatus, comprising:a carrier defining a longitudinal axis; abasket structure including at least three resilient shape memory splineshaving a normally curved configuration carried by the carrier, eachspline in the basket structure passing through a common plane orientedperpendicular to the longitudinal axis defined by the carrier, theresilient shape memory splines being arranged relative to one anothersuch that when the common plane is divided into four equal quadrants,each quadrant having a corner that intersects the longitudinal axisdefined by the carrier, at least one of the quadrants will have moreresilient shape memory splines passing therethrough than at least one ofthe other quadrants; and a plurality of electrodes on at least two ofthe resilient shape memory splines and no electrodes on at least oneresilient shape memory spline.
 16. An apparatus, comprising:a carrierdefining a longitudinal axis; a basket structure including a pluralityof resilient shape memory splines having a normally curved configurationcarried by the carrier, the resilient shape memory splines beingarranged relative to one another such that the radial spacing betweenone of the resilient shape memory splines and an adjacent spline on oneside thereof is different than the radial spacing between the oneresilient shape memory splines and an adjacent spline on the other sidethereof; and at least one electrode on at least one of the resilientshape memory splines.
 17. An apparatus as claimed in claim 16, whereinthe carrier comprises a catheter.
 18. An apparatus as claimed in claim16, wherein the plurality of resilient shape memory splines comprisestwo shape memory splines.
 19. An apparatus as claimed in claim 16,wherein the resilient shape memory splines define distal portions, theapparatus further comprising:a center stiffener associated with thedistal portions of the plurality of resilient shape memory splines. 20.An apparatus as claimed in claim 16, wherein the at least one electrodecomprises a plurality of electrodes on each resilient shape memoryspline.
 21. An apparatus as claimed in claim 16, wherein the pluralityof resilient shape memory splines comprises at least three resilientshape memory splines, the at least one electrode comprises a pluralityof electrodes on at least two of the resilient shape memory splines, andthere are no electrodes on at least one resilient shape memory spline.22. An apparatus as claimed in claim 16, wherein the plurality ofresilient shape memory splines comprises at least four resilient shapememory splines.